--> --> Unusually Well Preserved Tidal Signals and Tidal Constituents on Pliocene Paleo-Orinoco Delta, Trinidad

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Unusually Well Preserved Tidal Signals and Tidal Constituents on Pliocene Paleo-Orinoco Delta, Trinidad


The Orinoco Delta is one of few deltas where we can examine both modern and ancient tide records. The paleo-Orinoco delta succession (5My) on the Island of Trinidad contains both tide- and wave-influenced delta lobes within the same time slices, just like its modern analog. The tide-influenced delta lobes and estuaries exhibit some spectacular tidal signals. Middle to Late Pliocene tidal rhythmites have been examined in: (1) tidal channels from the upper part of Morne L'Enfer Formation at Cedros Bay; (2) estuary and delta lobe deposits at Erin Bay; (3) abandoned tidal channels associated with tide-influenced delta-front deposits from Telemaque Member of Manzanilla Formation at Matura Bay. Both wave and river current signals are also present in most of the study areas. In the alternating sand- and mud-dominated rhythmites, the preserved thickness of each lamina is directly and positively related to tidal current strength, sediment discharge, and seasonal changes, and also reflects environmental processes. Tidal constituent analysis of unusually well preserved paleo-Orinoco tidal rhythmites show four orders of tidal cycles from 10s of centimeters to several meters in scale. These are: individual diurnal or semi-diurnal tidal cycles (flood and ebb currents with slack-water periods); fortnightly tidal cycles (spring-neap); monthly tidal cycles (lunar perigee-apogee); and seasonal tidal cycles, delineating continuous records of tidal deposition on daily, semimonthly, monthly, and seasonal time scales. The constituent analysis not only highlights mixed semidiurnal tidal cycles, but also helps us determine whether the tidal constituent signals are mainly of Caribbean or of Atlantic tidal type. The tidal patterns that have been preserved in stratified rocks are the net result of multiple influences, not only the moon and the sun. The shape of bays and estuaries, geographic location, and weather patterns (local wind effects; monsoons), hurricanes and tropical storms, atmospheric pressure systems, temperature, and salinity all affect local tidal intensity. Keywords: Paleo-Orinoco Delta; Tidal delta; Rhythmites; Tidal constituents